1. Field of the Invention
The present invention relates to estimation of a Global Radius of Curvature (“GRoC”) induced by an edge sensor control system subject to displacements of a segmented mirror's boundary conditions. The present invention further relates to control of a segmented mirror's GRoC to within a prescribed tolerance using estimates of the GRoC.
2. Description of the Related Art
In general, segmented mirrors tiled with hexagons are used as primary mirrors for high powered telescopes and beam directors. Sensing and control of the segmented mirror's Global Radius of Curvature (“GRoC”) is used to maintain a figure of the segmented mirror to provide increased image quality. The GRoC is a low fundamental spatial mode of a segmented mirror. Thus, the GRoC has a low spatial frequency and a large magnitude when compared to any other shape or spatial mode of which the segmented mirror can attain. Therefore, the GRoC spatial mode is a significant contributor to the overall image quality attained by a telescope or beam director utilizing a segmented mirror.
Gonsiorowski, et al., U.S. Pat. No. 4,737,621, relates to an integrated adaptive optical wavefront sensing and compensating system. An optical Hartman-type technique is used to sense curvature of a wavefront sensor. The wavefront sensor is integrated with either a deformable or a membrane mirror. While targeted toward monolithic mirrors, Gonsiorowski, et al. does not use a segmented corrector.
Rather et al., U.S. Pat. No. 5,825,062, relates to an extendable large aperture phased array mirror system having a plurality of mirror segments. Rather, et al. relates to a PAMELA telescope residing in a testbed at NASA Marshall Space Flight Center. Rather, et al. senses all degrees-of-freedom with inductive edge sensors supplemented by a Shack-Hartman wavefront sensor. The Shack-Hartman wavefront sensor provides tile information to correct the curvature mode. Monolithic reflectors are replaced with arrays of segments that could be extended to fill a desired aperture.
Ulich, et al., U.S. Pat. No. 5,109,349, relates to an actively controlled segmented mirror. The segments of the mirror are continually adjusted with an active segmented mirror control to provide a reflecting mirror of large diameter. An array of sensors are used to measure differential position errors. Tilt sensors utilized as dedicated curvature sensors present an increase in cost of manufacture of the device.
Manhart, U.S. Pat. No. 5,113,064, relates to an optical method and apparatus for phasing segmented mirror arrays. All degrees of freedom, including curvature, are observable from the combination of Shack-Hartman sensors and edge-overlapping lenslet arrays. A special reference mirror is used to phase the inner ring of segments. Next, a second ring of segments is phased with the first ring. The progressive phasing technique of Manhart limits the ability to provide real-time figure maintenance.
Breckenridge, et al., U.S. Pat. No. 5,265,034, relates to a model for an optical system using feedback controlled optical wavefront compensation. An optical ray-tracing simulation model is used in order to generate a control gain matrix. A feedback control system uses feedback sensors to maintain alignment of the segments and a laser interferometer is used to sense a hinge angle between segments.